In the gas utility industry, it is often required that provision be made to detect attempts to tamper with gas meters, said attempts being either for the purpose of removing the meter to remove a gas blocking plate or to enable the use of gas directly from the supply pipe. For this purpose it has been common to enclose the nut which couples the meter to the supply pipe with a seal in the form of two halves which are fastener together with a lead and wire seal, or else said two halves are provided with means for snapping together in non-removable engagement.
The use of such devices has been limited by the cost thereof, and by the fact that it is often possible to remove such seals and replace them without evidence of tampering. It has also been difficult to detect whether a seal of the type in which the two halves are snapped together has been opened by breaking the fasteners and then gluing the two halves back together.